1. Field of the Invention
The present invention relates in general to vibration motors contained in cellular phones or pagers to constitute call incoming notification means together with a bell unit, and more particularly to a flat-type vibration motor which can continuously be driven stably owing to the removal of a nonconduction phenomenon resulting from a mechanical error occurring when it is driven in a two-phase half-wave drive manner.
2. Description of the Prior Art
A call incoming notification function is one of the essential functions of general communication units.
That is, the call incoming notification function is necessary for notifying a user of a communication unit of a call or message incoming situation, thereby allowing the user to receive an incoming call or message. The generation of a sound such as a melody or bell and the vibration of communication units are most used to effect the call incoming notification function.
In other words, if a desired call incoming notification function is previously selected by a user, it is performed upon call incoming, so that the user can recognize the call incoming state.
Among such call incoming notification functions, a vibration function is often used in consideration of saving other persons from suffering from noise pollution in places where many people are crowded.
A sounding function, such as the generation of a melody or bell, is generally adapted to output a preset one of various melodies or bells in a communication unit externally through a small-scale speaker so that the user can recognize the call incoming state. The vibration function is generally adapted to drive a small-sized vibration motor so as to transfer a vibratory force to a casing of a communication unit, resulting in the unit body being vibrated.
This invention relates to a vibration motor for performing the vibration function among the above call incoming notification functions. FIG. 1 is a cross-sectional view of a flat-type vibration motor, which is a representative vibration motor.
With reference to FIG. 1, the flat-type vibration motor comprises a lower casing part 1 provided at its bottom, and a shaft 2 fixed at the center of the lower casing part 1. Attached to the upper surface of the lower casing part 1 is a lower board 3 on which is printed a circuit capable of inputting external power.
The lower board 3 is typically fitted in small grooves of the upper surface of the lower casing part 1. An annular magnet 4 is mounted on the edge of the upper surface of the lower casing part 1 such that it is alternately polarized with N and S poles at regular intervals in a circumferential direction. The magnet 4 has an internal space at its center, which has its upper and lower parts opened and a predetermined diameter.
A pair of brushes 5 are provided on portions of the lower board 3 within the central internal space of the magnet 4 such that they are spaced apart from each other at a predetermined angle. The brushes 5 have their one ends connected respectively to input and output terminals and their other ends positioned at higher portions than the top of the magnet 4.
An upper casing part 6 is coupled with the lower casing part 1 at its edge to cover it. The upper casing part 6 supports the upper end of the shaft 2 while the lower casing part 1 supports the lower end of the shaft 2.
The shaft 2 and lower board 3 supported by the lower casing part 1, the magnet 4, the brushes 5 and the upper casing part 6 constitute a stator of the vibration motor. On the other hand, an upper board 7, a commutator 8 and a coil 9 constitute a rotor which is rotatable around the stator.
The upper board 7 is a printed circuit board formed by cutting a disc at a certain angle and supporting the resulting disc by the shaft 2 via a bearing 7a such that it is eccentrically rotatable.
The commutator 8 is formed integrally with the lower surface of the upper board 7 on which a circuit is printed, and has a plurality of segments supported by the shaft 2 via the bearing 7a. The brushes 5 are connected to the lower board 3 at their lower ends and brought into contact with the segments of the commutator 8 at their upper ends to elastically support them.
The coil 9 is attached to the upper surface of the upper board 7 on which no circuit is printed. This coil 9 may be provided with one coil or two or more coils according to a driving system of the vibration motor, for example, a single-phase driving system, two-phase driving system or three-phase driving system. In particular, the coil 9 may have two or more coils regularly and angularly spaced apart from each other. In FIG. 1, the coil 9 is shown to have two coils.
An insulator 7b is formed integrally with the remaining portion of the upper surface of the upper board 7 to which the coils 9 are not attached. The insulator 7b acts to electrically isolate the coils 9 from each other and increase an eccentric load. This insulator 7b is formed together with the commutator 8 and coils 9 attached to the upper board 7, through an insert injection process, when the upper board 7 is manufactured.
Accordingly, if an external voltage is applied to the lower board 3, it is induced to the commutator 8 through the brush 5 connected to the lower board 3 at its lower end, and then supplied to the coils 9 through the circuit printed on the upper board 7. As a result, an electromagnetic force is generated due to an interaction between a magnetic flux generated by the coils 9 and a magnetic flux generated by the magnet 4, so as to eccentrically rotate the rotor.
Subsequently, an eccentric rotation force of the rotor induces a lateral pressure, which is then transferred to the lower casing part 1 and the upper casing part 6 through the shaft 2. Because the lower casing part 1 is fixedly attached to a predetermined portion of a communication unit, the lateral pressure transferred to the lower casing part 1 causes the body of the communication unit to be vibrated. As a result, a user of the communication unit can sense the vibration of the unit.
A variety of driving systems have recently been proposed, although a three-phase driving system is generally applied to most vibration motors for the generation of a vibratory force. For example, a two-phase or single-phase driving system with a simpler construction is often used.
However, the two-phase or single-phase driving system has a disadvantage in that it cannot continuously maintain a driving force of a vibration motor, resulting in an instability in the driving of the vibration motor, differently from the three-phase driving system.
Namely, in the single-phase driving system, while a rotor is driven by an interaction between a coil and a magnet, a death point where the driving force is lost occurs at the moment that the flow of current through the coil is reversed in direction and thus changed in polarity.
In order to overcome the above problem, a cogging generator is typically provided in the single-phase driving system to generate an appropriate cogging at the death point, so as to continuously smoothly drive the vibration motor. However, this cogging generator is so very fine in size that it cannot always be accurately located at the same position.
Hence, the use of a cogging generator may reduce the motor productivity. Furthermore, for mass motor production, fine location deviations may occur in cogging generators, resulting in the occurrence of torque deviations in respective motors.
On the other hand, in the two-phase driving system, upon application of power, current must be induced in at least one of the two-phase coils 9 provided on the upper board 7. To this end, the brushes 5 brought into contact with the commutator 8 must always maintain a spaced angle therebetween constant.
In other words, assuming that the number of segments of the commutator 8, depending on the number of poles of the magnet 4, is n, the brushes 5 must maintain therebetween an angle obtained by dividing 360xc2x0 by n/2.
For example, the spaced angle between the brushes 5 must be 180xc2x0 if the number of segments of the commutator 8 is 4, as shown in FIG. 2, and 90xc2x0 if it is 8, as shown in FIG. 3.
In the case where the spaced angle between the brushes 5 is beyond a predetermined value, namely, it is smaller or higher than the predetermined value, the brushes 5 are connected respectively to the coils 9 with different phases, resulting in the occurrence of a nonconduction interval where no current flows to the coils 9.
Therefore, in the two-phase driving system, the spaced angle at which the brushes 5 are elastically brought into contact with the segments of the commutator 8 must accurately be maintained at a constant value depending on the number of the segments.
However, it is next to impossible to accurately form the brushes 5 at a certain angle therebetween during the actual motor manufacturing. This may cause a mechanical error to occur in the manufactured motor, which may in turn lead to the occurrence of a difference between drive performances of products and a large number of defective units for mass motor production.
Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a flat-type vibration motor wherein four-phase coils are attached to an upper board and connected in common to a neutral point, thereby exhibiting both a two-phase half-wave drive character and a four-phase drive character, irrespective of a spaced angle between brushes, and assuring a drive stability.
It is another object of the present invention to provide a flat-type vibration motor wherein the margin of a spaced angle between brushes brought into contact with segments of a commutator is guaranteed to facilitate the manufacturing of the brushes so as to increase a working efficiency.
In accordance with the present invention, the above and other objects can be accomplished by the provision of a flat-type vibration motor comprising a lower casing part; an upper casing part for covering the lower casing part; a shaft for interconnecting the lower casing part and upper casing part at their centers; a lower board attached to an upper surface of the lower casing part; a magnet mounted on an edge of the upper surface of the lower casing part outside the lower board, the magnet being polarized with at least 2 poles; an upper board formed by cutting a disc at a certain angle and supporting the resulting disc by the shaft via a bearing such that it is eccentrically rotatable; a commutator arranged on a lower surface of the upper board and around an axis of the shaft, the commutator having segments of the number twice that of the poles of the magnet; a pair of brushes having their one ends fixedly connected to the lower board and their other ends brought into contact with the commutator, the brushes being spaced apart from each other at an interval of an electrical angle within the range of xcfx80/2 to 3xcfx80/2; and coil means having a pair of armature coil assemblies formed on an upper surface of the upper board, which has the shape of the fan in a predetermined degree, each of the armature coil assemblies including a pair of armature coils duplicately wound and connected in common to a neutral point, the armature coils of the armature coil assemblies being sequentially conducted to have an electrical phase difference of xcfx80/2 in the order of their conduction.
Preferably, each of the armature coils of the coil means may have a pitch of an electrical angle of xcfx80.
As an alternative, each of the armature coils of the coil means may have a pitch of an electrical angle of xcfx80/2.